1. Field of Invention
The present invention relates to a method of manufacturing an inductor. More particularly, the present invention relates to a method of manufacturing a radio frequency (RF) semiconductor inductor with less substrate loss.
2. Description of Related Art
In general, an inductor is formed over a lossless substrate such as gallium arsenic substrate or a sapphire substrate which has a promising insulation effect to result in a low induced substrate current. Therefore, a high quality of the inductor can be obtained to enable an operation under a radio frequency (RF). However, since gallium arsenic substrate or sapphire crystal is expensive, a silicon substrate is typically used to reduce the cost. Using silicon technology to fabricate the inductor on a silicon substrate, though achieve a low cost fabrication, results in a higher consumption of energy. At present, methods to overcome the problem of high energy consumption by using silicon substrate have been developed. For example, the application of local substrate removal or slotted ground plane has been disclosed. However, these methods are not very practical and the effect is restricted.
The present invention provides an inductor formed on a silicon substrate that can effectively reduce induced current in the substrate, thereby reducing substrate loss.
In addition, the invention provides an inductor that has a higher inductance and a lower resistance. In addition, the parasitic capacitance of the inductor can be minimized value while the resonance oscillation frequency of the inductor can be raised to an optimum value.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for manufacturing a semiconductor inductor. A silicon substrate of a first conductive type is provided. A spiral conductive layer is formed over the silicon substrate. The spiral conductive layer has multiple spiral turns with a terminal at each end. One end of the spiral conductive layer is connected to an input terminal while the other end is connected to an output terminal. The spiral conductive layer can be made of aluminum or copper. A doped region of a second conductive type is formed in the substrate under the substrate surface. A doped region of the first conductive type is next formed in the substrate surrounding the doped region of the second conductive type. The doped region of the first conductive type is separated from the doped region of the second conductive type with a space without directly in contact. A reverse bias is provided to electrically connect the doped region of the first conductive type and the doped region of the second conductive type. A depletion region is thus formed between the doped regions of the first and the second conductive types. A top view of the dope region of the second conductive region has a sheet shape, while the doped region of the first conductive type has a ring shape surrounding the doped region of the second conductive type.
The invention also provides a method of manufacturing an inductor. A silicon substrate of a first conductive type is provided. A spiral conductive layer is formed on the silicon substrate. The spiral conductive layer has multiple spiral turns with a terminal at each end. One end of the spiral conductive layer is connected to an input terminal while the other end is connected to an output terminal. The spiral conductive layer can be made of aluminum or copper. A doped layer of the first conductive type is formed in the substrate under the spiral conductive layer. Concentration of dopants in the doped layer is higher than the concentration in the silicon substrate. The doped layer preferably has a depth of a few micrometers (xcexcm) and a dopant concentration of about 5xc3x971019 atoms/cm3.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.